But yeah, the system's not fit for the main series. It'd either be so easy that Pokemon Centers wouldn't be needed, or so hard that you'd be able to make it to a Pokemon Center before you recovered a significant amount. Poison would be a big problem too. It's understandable if a Pokemon faints from poison and is revived with an item because that item is medicine and has the ability to cure poison, but just walking around automatically recovering HP doesn't have that same effect.